The present invention generally relates to an implantable intravenous or endocardial lead for use with an implantable cardiac device, such as an atrial defibrillator. The present invention is more particularly directed to such a lead which is implantable within a vein or artery of the heart and which includes a steerable tip at the distal end of the lead to enable the lead to be steered along a desired path as the lead is implanted. The steerable tip may also include fixation means for retaining the lead within the artery or vein.
Implantable cardiac devices, such as pacemakers or defibrillators, are well known in the art. Such devices are configured to be implanted within a subcutaneous pocket beneath the skin of a patient and to be electrically coupled to the heart through one or more leads also implanted beneath the skin of the patient. Each lead includes at least one electrode which, when properly positioned within the heart or within a vein or artery of the heart, makes electrical contact with a desired portion of the heart for either sensing heart activity or applying a therapeutic electrical stimulus to the heart.
One such implantable cardiac device is an atrial defibrillator of the type, for example, described and shown in U.S. Pat. No. 5,207,219 which issued on May 4, 1993 in the names of John M. Adams, Clifton A. Alferness, Kenneth R. Infinger, and Joseph M. Bocek for "Atrial Defibrillator and Method for Providing Interval Timing Prior to Cardioversion", which patent is assigned to the assignee of the present invention and incorporated herein by reference. The atrial defibrillator described in that patent utilizes a first electrode positioned in the right atrium or superior vena cava of the heart and a second electrode positioned in the coronary sinus and great cardiac vein of the heart adjacent the left atrium. When the atria are in need of cardioversion, the atrial defibrillator applies cardioverting electrical energy between the first and second electrodes to cardiovert the atria.
The cardioverting pathway between the right atrium or superior vena cava and the coronary sinus and great cardiac vein has been shown to exhibit distinct advantages over previous pathways for cardioverting the atria. For example, by cardioverting the atria between the right atrium or superior vena cava and the coronary sinus and great cardiac vein, the cardioverting electrical energy is confined, in large measure, to the atria. This reduces the risk of undesirable side effects such as the inducement of ventricular fibrillation during atrial cardioversion. Also, it has been further found that this pathway reduces the energy levels required to cardiovert the atria resulting in less discomfort to the patient and less energy consumption by the defibrillator to thus extend its useful life.
One problem associated with the above-mentioned pathway is that it can be difficult to implant a lead for positioning an electrode within the coronary sinus and great cardiac vein. One method for implanting the lead and electrode, and as described in the aforementioned reference patent, includes passing the lead down the superior vena cava, through the right atrium, through the os or ostium (opening to the coronary sinus) and around to and into the great cardiac vein. This route unavoidably requires the lead distal end to be maneuvered around comers, past vein branches, and across constrictions in the coronary sinus and great cardiac vein.
Unfortunately, prior art leads do not incorporate any means to enable such corners, branches, or constrictions to be negotiated. Further, prior art leads have distal ends which are blunt and thus inherently difficult to properly implant and position. This is indeed unfortunate because if an electrode is not properly positioned, the intended therapy, whether pacing or cardioverting, can be severely compromised or even rendered ineffective altogether.
A further aspect of lead implantation, and particularly in the context of an intravenous lead such as one intended to position an electrode in the coronary sinus and great cardiac vein, is that the lead must also provide a means by which the lead, and hence the electrode, may be retained in the proper position. In the case of a coronary sinus and great cardiac vein electrode carrying lead, this is of great importance because the direction of blood flow through the coronary sinus is opposite to the direction of lead implantation. Hence, the blood flow through the coronary sinus tends to push the lead out of the coronary sinus, thereby resulting in lead dislodgement, rendering the lead nonfunctional.
One effective solution to this problem is fully described in co-pending U.S. patent application Ser. No. 08/002,138, filed Jan. 11, 1993 in the name of Clifton A. Alferness for "Coronary Channel Lead with Improved Fixation and Method", which application is also assigned to the assignee of the present invention and incorporated herein by reference. In accordance with one embodiment described in that application, the body of the lead is provided with a preformed resilient coiled configuration which, when released after implantation, expands to make continuous surface contact with inner wall surfaces of the artery or vein in which the lead is implanted. This serves to positively retain the lead in position while still providing a sufficient channel for blood flow through the coronary sinus.
Notwithstanding such an elegant solution for lead retention, alternative lead retention means may further be desirable. However, such lead retention means should not interfere with or otherwise hamper the implantation of the lead.
The present invention provides an endocardial or intravenous lead which successfully addresses each of the above-mentioned deficiencies of the prior art. The lead of the present invention includes a distal guide tip which, upon rotation of the body of the lead during implantation, serves to steer the distal tip end of the lead in a desired direction to readily negotiate corners, branches, and constrictions or the like. Further, the lead of the present invention includes fixation means formed in the distal guide tip for positively retaining the lead in its final position without impeding the implantation process.